I have been trying to get my car thru emissions testing for months with no luck. The car passes at idle, but fails at 2500(HC and CO both high.) One of the problems I'm having is holding the the RPM's at 2500. When I get the RPM's to 2500 it will stay there for only about 5 seconds and then drop about 500 RPM's and then it will work it's way back up to 2500 and begin the process all over again. The tester says I'll never be able to pass if the RPM's don't stay steady. One thing I have noticed is it doesn't happen when I first start the car(closed loop I suppose?) I have replaced fuel injectors, presssure regulator, fuel pump, sparkplugs and wires, and MAF. I"m running out of options and was wondering if anyone has any ideas before I take it to the shop?

 

Is there a check engine light or anything ? Im thinking it may be a bad Iac motor or dirty mass air flow.

 

No check engine lights and the MAF has been cleaned.

 

Would the IAC valve affect the RPM's at 2500 or only at idle?

 

Unplugged IAC and started engine. Idle RPM went to about 2000. Ran the throttle up to 2500 RPM and did not have any surging. Can I assume that the IAC is the problem?

 

Thats kinda weird that it would idle that high with the IAC unplugged. Have you checked for possible vacuum leaks?

 

I have only done a visual check and made sure that all the connections were good!